Although this invention is described herein particularly as it relates to the subject matter of the above identified U.S. Patent, it is not intended that use of the latching mechanism described herein be restricted solely to the particular downhole shut-in tool set forth in the patent. It is intended that the latching mechanism set forth herein find effective applicability with a wide range of downhole tools, including downhole shut-in tools such as are typically employed for bottom hole pressure measurement. When downhole well tools have been installed in wells such as in the production tubing tool actuation in most cases is achieved by inserting "running" tools into the well for latching onto an operative component of the downhole tool and achieving manipulation to shift the downhole tool to a desired operating condition. Such operations are typically carried out by wire line controlled tools in which a tool string is lowered into the well by a wireline system for actuation of the downhole tool.
In many cases well tools are intended to remain more or less permanently located within the tubing string of a well and in other cases, well tool are intended to be positioned in a mandrel of the tubing string for only a limited period of time for a specific purpose. Downhole shut-in tools may be permanently installed in wells and are operative within the tubing string of the well to temporarily shut-in the well so that certain activities such as bottom hole pressure measurement can take place. Regardless of the temporary or permanent nature of well tools, it is typically desirable to provide efficient mechanisms for traversing the tubing string of a well, latching onto operative components of the downhole tool and then shifting the downhole tool mechanism to a desired position. Subsequently it is desirable to return the downhole tool to its initial position and then effect efficient release of the wireline tool from its latched or secured position with the downhole tool and then removing the service tool from the well. This activity is known in the industry as "running" wireline tools. It is desirable, therefore, to provide an efficient mechanism for accomplishing operation of a downhole well tool which is located within a downhole tool mandrel such as is typically incorporated within a production tubing string. It is desirable to provide a mechanical latching mechanism that is capable of being operated by the dead weight of a wireline tool string to establish positive latching with the fishing neck of a downhole tool for operation thereof. It is also desired to provide an efficient mechanism for releasing the wireline tool string from the downhole well tool by simple application of linear tension force to permit efficient retrieval from the well.
Downhole well tools may be operated by controlling them with a running tool string which may be in the form of a wireline controlled tool running system or may conveniently take the form of a solid tool operating string such as may be composed of interconnected sections of tubing. In most cases downhole tools are serviced by wireline tool actuation systems. Well service tools may also be employed which are pumped through the tubing string to achieve upward or downward movement for latching to, operating and releasing from downhole well tools. It is also desirable, therefore, to provide a novel latching mechanism which may be employed in conjunction with fluid energized tool strings and which effectively permits latching to and actuation of downhole well tools by application of the dead weight of a tool running string and subsequently achieving effective unlatching of the tool within the tool mandrel of the tubing string upon application of tension. The latching device also permits efficient unlatching simply through upward application of force from the service tool string.